Liquid laundry detergent compositions contain surfactants to have good cleaning performance. However, many surfactant compositions cause skin and eye irritation. There are several methods to measure the skin irritancy potential of a surfactant composition.
One method to test the skin irritancy potential of a surfactant composition is Zein test. Zein score is measured using a Zein test (Gott, E., Aesthet. Medzin., Tenside 15: 313 (1966)). Zein test determines the extent of denaturation of Zein corn protein after exposure to a surfactant for a given period of time. Generally, the higher the Zein score, the greater the skin irritation potential.
Another method to measure the skin irritancy potential is corneosurfametry (CSM) test, a noninvasive quantitative test that measures the interaction between surfactants and human stratum corneum. (Pierard et al., Dermatology 189: 152-156 (1994)). Corneosurfametry involves removing a few layers of skin using cyanoacrylate skin surface strippings, short contact time with surfactants followed by staining the samples with fuchian dyes. A less damaged barrier allows greater penetration of the stain, therefore giving a more intense color, which is measured using colorimetrically with L*a*b* color space. This method is predictive of both protein and lipid damage in the skin. CIM (Color Indicator of Mildness) values are obtained from a corneosurfametry test. In a comparative study, the higher the CIM value, the milder the surfactant formulation.
A third method to evaluate the irritation effect of a surfactant formulation is measured by cytokine release of representative human skin model in response to the surfactant formulation. Where skin tissue viability is not decreased by 50% as compared to the negative control tissue (as measured by MTT reduction), the inflammatory potential is then measured by the production of the cytokines IL-1α and/or IL-1ra. MTT is a dye used to stain the skin cells called 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. In a comparative study, a lower cytokine release value means a milder surfactant formulation.
Consumers generally prefer mild liquid detergent formulations, and several products that claim to be mild are currently on the market. There is a still a need to develop improved mild liquid detergent formulations that have good cleaning performance.